DESCRIPTION: Toxoplasma gondii is a significant opportunistic infection of HIV/AIDS patients. Reactivated infection during immune suppression in AIDS causes a difficult to treat and life-threatening acute Toxoplasmic encephalitis. No treatment is currently available that can eradicate latent tissue cysts or prevent the risk of reactivated infection in HIV/AIDS patients. Itis essential to identify new strategies and new targets that have the ability to effectively prevent and treat recurrent infections in HIV/AIDS patients. Toxoplasma gondii strain type-dependent virulence mechanisms mediated by rhoptry proteins neutralize key mechanisms of host innate immunity that destroy intracellular parasites. The elucidation of parasite strain type-independent virulence factors could establish new drug targets for both acute and chronic infections caused by different parasite strain types. Dense granule GRA12 gene paralogs are highly conserved between different Toxoplasma strain types. We hypothesize that GRA12 gene paralogs are central regulators of virulence, stage differentiation, cyst biology, and infectivity. In specific im 1 we will use a targeted genetic approach to determine whether dense granule GRA12 gene paralogs are strain type-independent virulence factors. We will also determine whether GRA12 gene paralogs influence, or are associated with, rhoptry protein mediated virulence mechanisms. In specific aim 2 we will examine the role of GRA12 gene paralogs in cyst stage biology using in vitro and in vivo assays to address their functions in stage differentiation, cyst development, and chronic infection. This aim will also examine the hypothesis that GRA12 gene paralogs play an essential role in maintaining cyst burdens during chronic infection. Collectively, these aims explore key virulence and pathogenesis mechanisms of protein members of a newly identified GRA12 gene family. Thus, this high impact project will identify GRA12 gene paralogs as new drug targets to intercept acute and chronic phases of infection. This research project explores biology that is novel and carries fundamental importance for successful intracellular parasitism, stage differentiation, and transmission. Consequently, this R21 project holds extremely high innovation as well as the potential for a sustained, powerful impact in the field.